1. Technical Field
This invention relates generally to projection systems for providing head-up displays with which a user may both see information presented upon the display and see objects beyond the display, and more particularly to a laser-based head-up display having a wide field of view.
2. Background Art
Head-up displays are systems that present information to a user along a transparent screen so that the user need not move their eyes from their primary viewing position to read the information. Once only available in expensive systems such as military aircraft, head-up systems are now becoming commercially available to consumers as well.
Traditional head-up displays employ a projection source, such as a laser projector, to present images and information on a semi-transparent display surface, such as a windshield or cockpit bonnet. By projecting information onto a semi-transparent display surface, information can be communicated to a driver without the driver having to divert his eyes from his main point of focus—the road. Prior art projection sources generally use raster scanning techniques to superimpose lines of information to create a composite image.
One problem associated with prior-art head-up displays is that they have a limited “field of view.” The field of view, sometimes called the field of vision, is the angular extent of the display that is observable at any given moment. Most prior art automotive head-up displays are constrained to very narrow projection angles and consequently have a narrow field of view. The projection angles of many prior art displays are on the order of six degrees by two to three degrees. Consequently, when projecting information on a windshield, the information can only be written on a small projection surface, such as a square that is only a few inches wide. Attempting to project on a larger surface dilutes the light available from the projection source, thereby rendering the information unintelligible.
There is thus a need for an improved head-up display system having a wider field of view.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.